Do you really believe that their religion is the only common feature in the cultural environment of the people from the two countries you mentioned? Don't they both speak (more or less) the same language? Isn't there a great ethnic similarity between the peoples from these countries?
I am forced to come back to the example of Northern Ireland again to illustrate that, although the international media insisted on describing the conflict there as a religious war, adherence to a particular religion may indeed be only a minor part of a vast and complicated array of commonalities that constitute a cultural entity.